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All reviews: Advanced Groups Plugin

If you are using Groups or thinking about it- don't hesitate getting this plugin. I really needed the Category feature, and the Tags was an added bonus.
I purchased the plugin right after it was released, and the developer has been super responsive. Fixed an issue I had quickly. He even released an update for the Tags after we discussed a feature we needed.
(It really helped being able to see it in action on his demo site.)